This prospective epidemiolgic and neuropsychological study will examine the effects of early brain damage on selective aspects of cognitive and motor development. The specific aims are to investigate: (a) independent neuropsychological effects of localized neonatal white matter damage (WMD) and transient hypothyroxinemia (THP); (b) the role of other predictors of neuropsychological function (specifically, motor and sensory impairments and socioeconomic environment); (c) structural evidence of WMD at age 6 and associated neuropsychological outcomes; and (4)evidence of the plasticity of the developing brain in the presence of neonatal WMD. A sample of 487 surviving children from the Developmental Epidemiology Network (DEN) cohort of children born at very low birth weight will participate in the study at Columbia University. Additional children from the cohort will be examined at Children's Hospital in Boston. A sub-sample of 183 children will be recruited to participate in the MRI and from MRI, another sub-sample of 30 children will be recruited to participate in fMRI studies. After obtaining informed consent, as standard neurological evaluation, a comprehensive neuropsychological evaluation, and drawing of blood for lead and thyroid levels are done. The testing, which takes a full day, is done in English or Spanish, depending on the child's preference. While the child is being tested, a parent or guardian is requested to complete structured questionnaires about the child and their family. They are also asked to take a vocabulary test. Cranial MRI and fMRI studies will be done on selected children to identify evidence of WMD and brain plasticity following neonatal damage.